As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED OIL SPOTS ON HANGAR FLOOR. ENGINE WAS WASHED AND GROUND RUN FOR LEAK CHECK. INSPECTED ENGINE AFTER ENGINE RUN AND FOUND OIL ON BOTTOM SIDE OF OIL FILTER. FURTHER INSPECTION OF THE OIL LEAK REVEALED THAT THE OIL WAS LEAKING FROM THE HEX NUT ON THE BACK OF THE FILTER. (K)